With electric arc furnaces, especially for the manufacture of electrosteel, electrodes are used which possess substantial weight, especially in the case of large kettle sizes.
As a result of the efforts made recently to save energy, so-called combination electrodes have been proposed comprising an upper metallic permanent section and one or more active electrode sections composed of consummable materials. While the shaft-like upper metal section consists of copper or the like and has a cooling means, the active electrode sections are usually made from graphite. Combination electrodes of this type are, for example, shown in EP-OS No. 10 305 and EP-OS No. 12 537.
After the consumption of an active electrode section, replacement is necessary. For replacement, the electrode must be removed from the furnace. Because of the weight of the electrodes, handling generally can only be done with the use of a heavy lifting appliance, such as a gantry crane. After the removal of the electrode from the furnace, the spent active electrode section must be unscrewed from the permanent top or upper section and a new active electrode section must be screwed onto the permanent upper section. But these processes generally are only carried out using a suitable helping device due in part to the short time available, and taking account of the need for humane working conditions.
In the case of a conventional, totally self-consuming electrode made of graphite for example, devices are known for nippling a new section onto a partially consumed electrode shaft. However, the nippling of conventional electrodes is performed differently than with combination electrodes. With conventional electrodes, the nippling of a new active electrode section takes place mainly at the top end of a substantially consumed electrode slab or shaft, the substantially consumed shaft remaining in the furnace. A new electrode section is moved using a lifting appliance, such as a shop crane, to a position over the electrode slab which is held in an electrode holder positioned upon the furnace. Then the new electrode section is lowered onto the top end of the electrode slab in the furnace, so that a screw nipple arranged either on the lower end of the new electrode section or on the top end of the electrode slab is employed to couple the new section to the electrode slab. Nippling of the new electrode section to the top end of the electrode slab is accomplished by rotating the new electrode section.
A known device for nippling of conventional electrodes (DE-OS No. 16 90 556) consists of two cylinders co-axially arranged one inside the other. The inner cylinder is drivingly rotatable in relation to the outer cylinder. The inner cylinder includes at its lower end chucks which are radially pressable onto the electrode section being nippled. The outer cylinder can be torsionally supported for coupling against the electrode holder which is fixed upon the furnace. This device makes possible the mechanical nippling up of an electrode section on an electrode held in an electrode holder fixed on the furnace.
Such a nippling device is relatively costly in its design. It has two electric motors, one arranged above the inner cylinder and intended to clamp the electrode section to the electrode slab by axial movement between the two cylinders, the other motor arranged near the lower end of the device on the outer cylinder, for rotating, by means of a worm gear, the inner cylinder for the nippling up process. Such a design not only results in a very great height for the nippling device, but also results in a large diameter near the furnace. The latter factor has proven to be especially disadvantageous for the operation of the device. In addition, when clamping the electrode section, the inner cylinder formed as a clamping bush has to be displaced in the direction of its longitudinal axis against a surrounding conical ring, so that the chucks may mechanically damage the new electrode section, at least at the start of the clamping motion causing possible subsequent fissure formation in the electrode.
To eliminate these disadvantages, the two cylinders and a third cylinder have been co-axially mounted (DE-AS No. 24 18 688), and guided for clamping of the new electrode section to be nippled in a longitudinal direction by a threaded nut, rotatable via a rack-and-pinion or a chain drive employing a motor arranged near the top portion of the outer cylinder. The motor, for nippling up of the electrode section, effects rotation of the intermediate cylinder and of the inner cylinder which is fixed thereto employing torsional strength, for which purpose a detent securing the inner cylinder against rotation during the chucking process is released.
Because of the design described above, such a device has an external diameter near the furnace which only slightly exceeds the electrode diameter. Moreover, the chucking and nippling up are accomplished employing only one joint motor, which it located at one side of the head of the device. While achieving a reduction in size, the overall height of the device is still relatively large, since the new electrode section to be newly nippled up is clamped at its lower end, the height of the device being still substantially larger than the length of the new electrode section. With the device in question, having the material disadvantage that three cylinders are provided each possessing the required lengths, the device is not only very costly in materials, but also is correspondingly heavy.
Both such nippling devices above have a common drawback; the new electrode section is grasped by a chuck which contributing to a complicated design for the entire device and moreover making difficult the acceptance of a new electrode section in the nippling up device, since the new section must be exactly aligned with the nippling device which must then be exactly thrust over the electrode section.
In a further known nippling up device (DE-OS No. 23 38 741), the electrode section to be connected with the electrode can be firmly clamped in a holding ring which is rotatable and adjustable for height with respect to the electrode holder on the furnace side. A support frame holds a support ring guided on the frame by suspension means. The support ring carries a drive means by which an electrode ring, suspended on the support ring and including a hydraulically actuated clamping means arranged on its periphery, is rotatable employing an interposed ring gear secured on said holder ring against the support ring. The holder ring is axially displaceable between the electrode and the electrode section corresponding to the thread pitch of the nipple connection. The suspension means is displaceable transversely to a longitudinal axis of the electrode and the support frame, designed with its relevant components as a portable unit, is provided with guide portions, by means of which it can be connected in a precisely defined position relative to the electrode holder. After completing the nipple connection between the electrode and the new electrode section, the nippling up device can, after releasing the holder ring clamping means, be lifted from the electrode holder employing a lifting appliance and can be used elsewhere.
But such a device also has a relatively complicated design due in part to a costly clamping means and in part to the special support frame needed for the support ring and for the holder ring. Consequently, the diameter of the device perpendicular to the axis of the electrode is substantially enlarged which can make operation of the device more difficult.